Initial stages of epitaxial growth of Y-stabilized ZrO2 thin films on a-SiOx/Si(001) substrates

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Abstract
The initial stages of crystallization and growth of epitaxial Y‐stabilized ZrO2 (YSZ) thin films on Si (001) substrates covered with amorphous native oxide were investigated by transmission electron microscopy (TEM) and reflection high‐energy electron diffraction (RHEED). The YSZ crystallizes by solid‐phase epitaxy with an initial thickness of 1 nm. The crystallization is initially incomplete, yielding both epitaxial and disordered regions of the YSZ film. In situ RHEED measurements showed the lattice parameter of the YSZ gradually decreased during growth, reaching the bulk value at a film thickness of 5–7 nm. For a larger thickness, the film is fully elastically relaxed. TEM revealed misfit dislocations at the YSZ/Si interface. The average spacing between misfit dislocations with Burgers vector b=1/2 〈110〉 was measured as 8.3 nm, showing epitaxial misfit strain to be fully accommodated by misfit dislocations. Thermal strain introduced during cooldown from the deposition temperature is fully elastically accommodated. For YSZ thicknesses below 7 nm, the thickness of the regrown layer of silicon oxide at the YSZ/Si interface is 0–0.5 nm.